Adjustable office seats and chairs are certainly well-known. To enable a more comfortable seating position than lower-priced models, which are usually fixed, they incorporate, in addition to a device for adjusting the height of the seat, the use of a device for the controlled swinging of the seat back, generally located in the part immediately beneath the seat plane and integral to it. This device is primarily activated via a protruding lever that can easily be gripped and therefore rotated in one direction or another, until the internal mechanism releases the articulation.
In short, it is therefore possible to maintain that the following are known:                1. chairs in which the seat and the seat back are designed with separate body shells, which are connected in such a way that an inclination of the seat back corresponds to a parallel downward movement of the seat plane;        2. chairs in which only the seat back is freely swinging;        3. chairs in which the raising of the seat plane corresponds to the inclination of the seat back;        4. chairs in which both the seat and the seat back are individually adjustable;        5. finally, seats in which both the seat plane and the seat back, which are interconnected, perform a synchronized swinging movement.        